Tire intended for heavy loads and to be inflated to a high pressure

ABSTRACT

The present invention relates to a tire (P) intended to bear heavy loads and inflated to high pressure, particularly suited for use as an airplane tire. In order to improve the fatigue strength of the beads (4), the axially outer plies (3E, 3F) of the carcass reinforcement (3) in the region of the beads (4) have their edges (30E, 30F) disposed between the upturns (30A, 30B, 30C, 30D) of the axially inner plies (3A, 3B, 3C, 3D).

BACKGROUND OF THE INVENTION

The present invention relates to tires with radial carcass reinforcementintended to bear heavy loads and to be inflated to relatively highpressures, and particularly to tires suited for use as airplane tires.

The radial carcass reinforcements of such tires generally have severalplies of textile cables which are anchored in each bead to at least onebead wire and generally to a single bead wire. The reinforcementelements of these tires are wound around said bead wire from the insideto the outside, forming upturns the ends of which are spaced radiallyfrom the axis of rotation of the tire. The severe conditions under whichairplane tires are used, and, in particular, the overloads imposed, aresuch that the fatigue strength endurance of the beads is slight,particularly at the place of the ends of the upturns of the carcassreinforcement.

A substantial improvement in performance is obtained by separating theplies of the carcass reinforcement into two groups. The first groupcomprises the axially inner carcass reinforcement plies in the region ofthe beads, these plies being then wound around a bead wire in each beadfrom the inside to the outside of the tire. The second group is formedof at least one axially outer ply in the region of the beads, which plyis generally wound around the bead wire going from the outside to theinside of the tire.

Such arrangements are known and are shown, for instance, in U.S. Pat.No. 4,244,414 (FIG. 2).

The fatigue strength of the beads formed in this manner is, however,still insufficient and this lack of fatigue strength results inseparations between the outer plies and/or the last outer ply and therubber which covers it, this rubber forming the outside of the beadand/or of the side wall; these separations are generally accompanied byfatigue of the cables of these plies.

SUMMARY OF THE INVENTION

The present invention proposes a solution in order to improve the lifeof the beads of the tires concerned while using bead wires having insidediameters as small as possible, which permits better resting on theflanges of the rim, this solution comprising arranging the edge (edges)of the axially outer ply (plies) between the upturns of the axiallyinner plies, without winding around the bead wires.

The present invention relates to a tire, intended for heavy loads and tobe inflated to high pressures, particularly suited for use as anairplane tire, having a tread, a crown reinforcement, and a radialcarcass reinforcement comprising at least two axially inner plies oftextile cords, wound around a bead wire in each bead from the inside tothe outside of the tire and then forming upturns, and at least oneaxially outer ply of textile cords superimposed on the inner plies belowthe crown reinforcement and separating said plies in the beads in orderto extend along the upturns in the beads, characterized by the fact thateach of the outer plies has its edges arranged between the upturns oftwo adjacent inner plies and by the fact that the ends of the axiallyouter ply (plies) are disposed axially to the outside of a straight lineperpendicular to the axis of rotation of the tire and tangent to thecircle circumscribed on the bead wire, axially on the outer sidethereto, while remaining situated radially to the outside of a straightline parallel to the axis of rotation, tangent to the circlescircumscribed on the cross sections of the bead wires at their pointsradially closest to the axis of rotation.

In the case of a plurality of axially outer plies, a uniformdistribution of the tensions on these plies is also obtained. For thesame purpose, the ends of the upturns of the axially inner plies arepreferably spaced from the base of the bead by a height at least equalto 0.25 times the height of the tire mounted on its service rim,inflated to its service pressure, said height being measured at thelevel of the center line of the radial carcass reinforcement.

In the same way, the said upturns have radially spaced ends, thedifference between the radial distances of the ends of two adjacentupturns being at least equal to 0.03 times the height of the tire on therim, the radial distances being all different from each other.

Furthermore, the common distance or radial distance of junction betweenan axially outer ply and the two axially inner plies which surround itthat is to say, the radial overlap between the end of the outer ply andthe closest end of an adjacent inner ply, is advantageously greater than0.15 times the height on the rim of the tire.

The presence of sufficiently long upturns as well as the fact that theirends are spaced radially makes it possible also to obtain a certainadvantage, namely to increase consequently the value of the testpressure which the airplane tire must withstand. If one recalls that thetest pressure must be equal to four times the service pressure, it isthen possible to increase the inflation pressure used for the tire innormal service or, which is preferable, to lighten the tire whileretaining the constant service and test pressures.

The life of the beads is further improved if the longest upturn is thatof the first axially inner ply and the shortest upturn that of the lastaxially inner ply, all the upturns being spaced by the same radialdistance.

Preferably, the ends of the axially outer ply or plies are disposed onthe inside of a second straight line parallel to the axis of rotationand spaced radially from the first straight line tangent to the circlescircumscribed on the cross sections of the bead wires at their pointsradially closest to the axis of rotation by an amount equal to twice thediameter of the circles circumscribed on the bead-wire cross sections.

DESCRIPTION OF DRAWING

The invention will be better understood by means of the followingdescription, read with reference to the diagrammatic drawing, which isgiven by way of example. In this drawing, FIG. 1 is a sectional view ofa bead of a tire in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The example given is that of an airplane tire of size 46×17.0 R 20,mounted on a standard rim of size 13.25×20 (standards of the Tire andRim Association). The carcass reinforcement 3 is formed of six carcassplies 3A to 3F of textile cords.

Among these six plies, four axially inner plies 3A to 3D are wound ineach bead 4 around a bead wire 5 of circular cross section from theinside to the outside of the tire P, forming upturns 30A to 30D. Theends of these upturns are spaced from the base of the bead, representedby a line XX' parallel to the axis of rotation of the tire and passingthrough the point of intersection of the vertical wall of the bead andthe frustoconical generatrix of its seat by the respective heights h₁,h₂, h₃, h₄. The greatest height h₁ is the height of the upturn 30A ofthe first axially inner ply 3A, while the smallest height h₄ is theheight of the upturn 30D of the last axially inner ply 3D, theintermediate heights h₂ and h₃ being those of the upturns 30B and 30C ofthe intermediate plies 3B and 3C. These heights h₁ to h₄ are equal to33%, 38%, 43% and 48%, respectively, of the height H of the tire on therim, equal to 290 mm.

By definition, the height (not shown) of the tire, mounted and inflated,is the radial distance measured between a line parallel to the axis ofrotation passing through the top point of the center line of the carcassreinforcement and a line parallel to the axis of rotation, spaced fromsaid axis by an amount equal to the standard nominal radius of theservice rim.

The axially outer carcass plies 3E and 3F have their edges 30E and 30F,which are disposed between the upturns 30C and 30B, respectively, of theinner plies 3C and 3B and the upturns 30C and 30D of the plies 3C and3D. The ends of these plies 3E and 3F are located, seen in meridiansection, axially to the outside of the line YY' perpendicular to theaxis of rotation of the tire, and therefore to XX' and tangent to thecircle circumscribed on the bead wire 5 at its point axially furthesttowards the outside. They are located radially at the level of the beadwire 5 between the straight line D parallel to the axis of rotation ofthe tire and tangent to the base of the circle circumscribed around thebead wire 5 and the straight line D' parallel to D and spaced radiallyfrom D by the amount 2d, d being the diameter of the bead wire 5.

As compared with a tire of the same size having a carcass reinforcementwith the same number of axially inner plies and the same number ofaxially outer plies, but the outer plies of which cover the upturns ofthe inner plies, as shown, for instance, in FIG. 2 of U.S. Pat. No.4,244,414 mentioned above, the tire of the present invention, underconditions of equal load of 19,600 kg and an inflation pressure of 14.8bar completed 3,000 cycles, namely about 30% more than the control tire,which completed 2300 cycles, the travel being effected on a flywheel anda cycle reproducing a phase of travel under load followed by a phasewith elimination of the load.

Furthermore, the tire of the invention has a bursting pressure which is15% greater than the bursting pressure of the control tire and fargreater than the normal test pressure for the size in question.

We claim:
 1. A tire, intended for heavy loads and to be inflated to ahigh pressure, having a tread, beads containing bead wires, a crownreinforcement and a radial carcass reinforcement comprising at least twoaxially inner plies of textile cords, wound around a bead wire in eachbead from the inside to the outside of the tire and then formingupturns, and at least one axially outer ply of textile cordssuperimposed on the inner plies below the crown reinforcement andseparating said plies in the beads in order to extend along the upturnsin the beads, characterized by the fact that each of the outer plies isdisposed between the upturns of two adjacent axially inner plies, and bythe fact that the ends of the outerplies are disposed axially to theoutside of a straight line (YY') perpendicular to the axis of rotationof the tire and tangent to the circle circumscribed on the bead wire atits point axially furthest to the outside, and radially to the outsideof a straight line (D) parallel to the axis of rotation of the tire andtangent to the circles circumscribed on the bead wires at their pointsclosest to the axis of rotation.
 2. A tire according to claim 1,characterized by the fact that the ends of the upturns of the innerplies are spaced from the base of the beads by a height at least equalto 0.25 times the height H of the tire on its rim, measured at the levelof the center line of the carcass reinforcement.
 3. A tire according toclaim 2, characterized by the fact that radial distances h₁, h₂, h₃, h₄separating the ends of the upturns from the base of the beads aredifferent from each other, the difference between two of these distancesbeing at least equal to 0.03 times the height H of the tire on the rim.4. A tire according to claim 1, characterized by the fact that thecommon radial distance between an axially outer ply and the two axiallyinner plies which surround it is at least equal to 0.15 times the heightH of the tire on the rim.
 5. A tire according to claim 2, characterizedby the fact that the first axially inner ply has upturns the ends ofwhich are separated from the base of the beads by a height h₁ which isthe largest, equal to 0.5 H, the second axially inner ply has upturnsthe ends of which are separated from the base of the beads by a heighth₄ which is the smallest and is equal to 0.25 H, h₂ and h₃ being therelative distances to the ends of the upturns of intermediate plies suchthat h₁ >h₂ >h₃ >h₄.
 6. A tire according to claim 1, characterized bythe fact that the ends of the edges of the outer plies are disposedradially to the inside of a straight line (D') parallel to the straightline (D) which is tangent to the innermost point of the circlecircumscribed on the bead wire and spaced radially from said tangentialstraight line by an amount equal to 2d, d being the diameter of thecircle circumscribed on the cross section of a bead wire.